1. Field of the Invention
The invention relates to a device for flow-injection analysis, comprising a reaction loop, one or more pumps, an injection valve, one or more detectors and an evaluating device.
2. Brief Description of the Prior Art
Flow-injection analysis (FIA) is a wet-chemical analysis method which in recent years has developed into a valuable and frequently used method. In flow-injection analysis, the sample to be analysed is injected into a stream of a suitable liquid (carrier liquid) and is introduced, together with the latter, into a detection system. The structure of a device for flow-injection analysis is therefore similar to that of a liquid chromatography arrangement, the separating columns being replaced, however, by a reaction loop. The (generally peristaltic) pump serves to drive the carrier liquid. The sample to be analysed is injected through the injection valve (generally a rotary 2- or 3-way valve) into the carrier liquid. The detector indicates the passage of the sample, and in the evaluating device the analytical content of the sample is detected quantitatively. This functional principle is illustrated diagrammatically in FIG. 1 (from J. Ruzicka and E. H. Hansen `Flow Injection Analysis` in `Chemical Analysis`, Volume 62, John Wiley and Sons, New York, 1981), R being the carrier or reagent stream, S the site for injection of the sample, FC a through-flow cell and W the liquid waste. In the simplest method of flow-injection analysis the carrier stream might contain a reagent that reacts with the substance to be analysed to form dyestuff. An analysis reaction could be, for example, the expulsion of thiocyanate from Hg.sub.2 (.sup.I) (SCN).sub.2 by Cl.sup.- ions. After the addition of Fe.sup.3+ ions a blood-red coloring is produced and the photometer measures a wave-length of 480 nm. Although flow-injection analysis is not a continuous method of analysis, the repetition rate of the individual measurements is generally so high that for many purposes the method can be regarded as a quasi-continuous method.
Flow-injection analysis is not limited to applications in which a sample to be analysed is injected into a stream of liquid containing a reagent. With expensive reagents, it may be more advantageous to inject the reagent into the sample. If the reagent and the sample are expensive, the sample and the reagent can be injected simultaneously into a stream of carrier liquid by way of a dual-input valve. This is known as the `Merging Zone` method.
It is not only photometers, as mentioned above, that are suitable as detectors but in fact any device that converts the chemical detection reaction quantitatively into an electrical signal. Detectors may be, for example, fluorimeters, refractometers, luminescence detectors, turbidity meters, pH and ion-sensitive electrodes, voltage-measuring and amperometric detectors, conductivity meters, thermistors, semi-conductor structures (FETs), etc.. Flow-injection analysis is not limited to wet-chemical detection means. The use of enzymes in dissolved or immobilized form, of immobilized antigens/antibodies, of organelles and of microorganisms means that the range of application of flow-injection analysis can be considerably extended.
Some known devices for flow-injection analysis are described in more detail below.
A basic device (type 5020) available from Tecator GmbH, 6054 Rodgau, comprises two multi-channel peristaltic pumps, an injection valve, a module for mixing the sample and reagent streams and a microprocessor control means, with the aid of which the analysis procedures can be preprogrammed. A diffusion stage, an extraction stage and a thermostat for heating the reaction loops can be added subsequently. A sample-input machine as well as a recorder and a printer can be connected externally. Depending on the mode of operation, the detector signal is evaluated in particular ways, for example the signal height, area, width and building-up time can be evaluated. The pumps, the injection valve and the control electronics are mounted in the device in a fixed manner. The housing dimensions are approximately 45 cm.times.45 cm.times.20 cm. If a multi-channel arrangement is used, a corresponding number of individual devices have to be arranged adjacent to one another.
A further known device for flow-injection analysis, from Chem Lab, has a 5-channel pump, an injection valve, heating devices for the reaction loops and a filter photometer with glass fiber optics and a through-flow cell, which are mounted in a fixed manner in a housing having the dimensions 30 cm.times.38 cm.times.18 cm. A recorder and a microprocessor can be connected to the photometer. An extension in the form of an autosampler and an optional coupling to a recorder and/or a data-detection and evaluation system are possible. If a multi-channel arrangement is to be used a plurality of complete devices have to be set up next to one another.
Hitachi also offers a basic device (dimensions 30 cm.times.40 cm.times.55 cm, Type K-1000) that contains, mounted in a fixed manner, a two-channel piston pump, a four-channel peristaltic pump, an injection valve and temperature-controlled reaction loops. An automatic sample indicator, a solvent-extraction unit and optical detectors (photometers, fluorescence spectrometers) can be connected externally. After-fitting with printers, plotters and data stations is possible. Multi-channel operation with the basic device alone, on the other hand, is not possible.
Flow-injection analysis can, as already mentioned, be used for a wide range of applications. The flexibility of the devices currently on the market is, however, unsatisfactory and not all the devices needed for analyses are available, for example enzyme reactors and detectors other than photometers. In addition, the desire for a multi-channel structure is on the increase and cannot be very adequately catered for with the known devices.
The problem on which the invention is based, therefore, is to provide a versatile device for flow-injection analysis which can be used for a variety of applications and which is economical to produce.